<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{padding: 0;margin: 0;}
        .row::after{
            content: "";
            display: table;
            clear:both;
        }
        ul{
            list-style: none;
           
            line-height: px;
            background: pink
        }
        li{
            float:left;
            width: 100px;
            text-align: center;
        }
        li:hover{
            background: deeppink;
        }
        .drop-menu{
            position: relative;
        }
        .drop-content{
            position: absolute;
           width: 100px;
           background: red;
           display: none;
        }
        .drop-content a{
            text-align: center;
            display: block;
            
        }
        .drop-menu:hover .drop-content{
            display: block
        }
    </style>
</head>
<body>
    <ul class="row">
        <li class="drop-menu">1
            <div class="drop-content">
                <a href="#">1.1</a>
                <a href="#">1.2</a>
            </div>
        </li>
        <li>2</li>
        <li>3</li>
    </ul>
</body>
</html>